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need some advice on soldering tiny terminals

Desert Rat

Well Known Member
This particular skill set isn't something I've had a lot of practice with, and I'm trying to solder leads on the little $2 PTT switch that Stein sells, without much success.

I've ruined 2 of these darn things so far. By the time the solder flows, the plastic terminal base where the terminal tabs come out of is also flowing, and that's the end of that.

On the first one I tried heating up the terminal and wicking the solder though the wire to it. Pretty obvious that was the wrong thing to do.

On the second attempt, I tried heating up the wire a little further away from the switch and wicking the solder the other way, away from the switch housing. Still melted :(

I'm using a cheap weller pencil style soldering iron with a fine tip if that matters, and I've tinned it before use.

Any tips?

https://www.steinair.com/product/momentary-push-button-switch-14-red/
 
Soldering small leads

The soldering iron may be at the incorrect temperature, as mentioned above. A temperature controlled iron is the best way to go.
Also confirm that you are using very thin 60:40 solder for electronic work? It is about 0.7-1.0 mm in diameter.
Otherwise, work technique = good lighting, magnification if your eyes need it, something to hold the parts, and a rest for your arm. Touch the solder on the terminal at the tip just as soon as the tip heats up the terminal. Shouldn't take longer than 1.5 seconds to heat+flow+remove iron.
 
I have a soldering station similar to this one, and a small assortment of tips:

https://smile.amazon.com/Hakko-FX88...sprefix=hakko+soldering+station,aps,79&sr=8-2

Also BE SURE to use the right lead / tin solder with flux. The "more environmentally acceptable" lead-free stuff doesn't melt/flow as well.

I like the Kester brand, something like this:

https://smile.amazon.com/Kester-83-...jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

Be sure to secure wire onto the lugs so that it doesn't move when soldering. If you're doing this on a bench, something like this can help secure stuff while soldering:

https://smile.amazon.com/Helping-So...=hi&sr=1-2&store_ref=SB_A05669653AVXPJPJVHEHI
 
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Also BE SURE to use the right lead / tin solder with flux. The "more environmentally acceptable" lead-free stuff doesn't melt/flow as well.

I like the Kester brand...

Big yes! Also, cheap / no-name solder might say on its label it is good ol' 60/40, but what it actually is, nobody knows. I thought I cannot solder until I bought Kester, it worked so much better. My personal preference is 63/37 solder for its eutectic properties (does not have this intermediate state where it is neither fully liquid nor fully solid).
 
most important trick is keeping the tip clean, so that liquid solder will stick to it. Look for areas with no liquid solder on it and second is keeping a large enough ball of solder for heat transfer. A novice will just put the iron on the wire and wait for everything to get hot enough and with poor heat transfer, everything gets really hot before the terminal/wire reaches the correct temp for capillary flow.

First, it is critical that the portion of the tip that is touching the wire has liquid solder on it (it wont if it has burnt resin on it - In that case, scuff the tip with sandpaper back to copper or metal and re-tin it). As soon as you put the tip on the wire, dab the solder in there and insure that there is liquid solder between the tip and wire. This will accelerate the heat transfer by a large order and allow you to get capillary action on the terminal without melting the housing. You can also touch the solder to the iron to get a little ball on it and then touch the iron to the wire.

after some use, a copper tip will have pockets eroded into it's surface that can be hard to see, as they are filled with burnt resin. In these cases, take it to the grinder and make it a good cone again. These pits also prevent good heat transfer. This is why a good iron has a long tip with a screw holding it in place.

Larry
 
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Most Weller irons have tips that are available in different temperatures. You may be able to find a lower temp tip that will work for you. I find the flattened (shovel) tips work the best. You should make sure the switch and the wire are secured and you should be able to get the solder to reflow pretty quickly. If you are messing around trying to hold the wire and the switch then you may end up overheating the switch. Make sure you have a clean tip. Then tin the tip by putting a little solder on the tip and then wipe it off using a damp sponge. In a bind it could just be a wet paper towel. Once you have prepped the tip this way quickly move on to soldering the connection.
 
it wont if it has burnt resin on it - In that case, scuff the tip with sandpaper back to copper or metal and re-tin it

I would add a bit of caution here: it depends on the type of the soldering iron tip. Check your manual, if you have one.

"Older" soldering irons used to have a solid copper tips, which you would sand as needed to clean / remove pitting. However, modern soldering stations tend to have tips with some iron plating over them.

The way you are supposed to clean these tips is either by using a damp sponge (oftentimes comes with a soldering station, you wet it before the use) or use a brass/metal sponge.

But yes, clean tip which solder can stick too is critical: it helps to transfer the heat much faster to the joint the whole process is much shorter and you don't parts too much.
 
Send it to Steinair

Pay Steinair to do the work and save yourself the headache and grief. I'm sure they can help you out at a very reasonable, cost.
 
Lots of tips here, I'll add one more....

For sensitive or hard to solder joints, pre-tin (i.e. coat with a thin layer of solder first) the two pieces to be joined. You can pre-tin quickly with little heat added to the part when not worried about joining the two pieces.

Let the pieces cool.

Solder by re-melting the two tinned pieces together with a quick application of heat.

Of course making sure the soldering iron tip is clean and coated with shiny solder as noted above.
 
Put some flux on the wire and the terminal. Let the tip heat up fully, so that it melts the solder almost the second it touches it. Then get a small drop of solder on the tip and touch the melted solder to the joint. The melted solder should almost instantly wick into the wire and joint. Remove the tip and let cool.
 
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